The present invention relates generally to telephone switching systems, and in particular, to a telephone switching system based on a fiber optic switch fabric using wave division multiplexing.
Modern telephone switching systems are large-scale, highly complex systems incorporating one or more switching elements cooperatively controlled and supervised by one or more computing means. One commercial exemplar of a modern telephone switching system is the 5ESS(copyright) ELECTRONIC SWITCHING SYSTEM, from Lucent Technologies Inc., 600 Mountain Avenue, Murray Hill, N.J. 07974. The 5ESS(copyright) electronic switch is a distributed switching system. Both the switching system capabilities and the control, supervision and administration capabilities are distributed. Each of the computing facilities associated with these distributed modules includes appropriate computer programs or software to achieve the desired operation of the switching elements and other components of the switching system.
The distributed switching modules are interconnected by a central fabric called a time-multiplexed switch. The time-multiplexed switch provides a means for the connected switching modules to communicate with each other. The number of links that can be connected to the time multiplexed switch controls the number of switching modules that are interconnected and ultimately, the size of the switch. Though sufficient to meet current needs, the limitations of the central fabric are challenged by trends such as (1) Internet access; (2) networks with edge remote access vehicles; (3) the change in network traffic from predominately voice to a mixture of voice, data, fax and video; and (4) transport protocols such as ATM, SONET, and TCP/IP.
Therefore, an evolution of the central fabric switch is required to further the distributed switching architecture without losing the scalability accomplished by interconnecting switching modules.
The limitations of the time-multiplexed switch central fabric are overcome and an improvement in the switching architecture is achieved with the use of a plurality of optical links between switching modules. The switching modules use wave division multiplex technology to communicate with each other over the optical links.
A method for switching telephone calls using wave division multiplex switching includes the step of receiving a call and determining a destination switching module that is to receive the telephone call. After the destination switching module is chosen, a wavelength of optical spectrum of the fiber optical cable interlinking the switching modules is allocated to carry data associated with the telephone call. The allocation may be a fixed allocation. That is, a wavelength may be dedicated to connecting one switching module to another switching module. Alternatively, the wavelength may be dynamically allocated with the allocation being communicated between the involved switching modules. After the wavelength is determined, data associated with the telephone call is transmitted between switching modules over the allocated wavelength.
In another arrangement, wavelengths of spectrum of an optical cable coupled to a plurality of switching modules are allocated such that a wavelength is dedicated for a connection to one of the plurality of switching modules from every other one of the plurality of switching modules. The plurality of switching modules communicate with each other by sending communications over the optical cable using the allocated wavelengths. The plurality of switching modules selectively demultiplex the optical communications to retrieve the wavelengths allocated to communications for the receiving switching module.
A telephone switching system in accordance with the invention includes a plurality of switching modules. An optical ring interconnects the switching modules. The switching modules communicate telephone calls to each other over the optical ring. Each switching module includes a wavelength transmitter that transmits optical signals having a certain wavelength of an optical spectrum over the optical link. Each switching module includes a wavelength demultiplexer that selectively receives certain wavelengths of an optical spectrum from the optical link. Preferably, a control processor is coupled to the wavelength transmitter and wavelength demultiplexer to allocate telephone calls through the switching modules to certain wavelengths for transport over the optical link.